Sheet metal stretching tool



Feb. 18, 1969 T N 3,427,850

SHEET METAL STRETCHING 001;

Filed Feb. 7. 1966 INVENJ'QA JACOB ANTONv Me me vs United States Patent5 Claims Int. Cl. B2111 11/02, 1/04, 41/02 ABSTRACT OF THE DISCLOSURE Asheet metal stretching tool having a pair of clamps, each of which has amovable jaw element and a fixed jaw element, mounted on a rigid guide,at least one of the clamps being movable longitudinally of the latter.An extensible jack positioned between the movable jaw elementssimultaneously moves the latter into a gripping position relative to thefixed jaw elements and moves the clamps apart.

This invention relates to tools for stretching sheet metal, particularlyto the stretching of automotive door and trunk panels to aid in theremoval of dents and other deformations therefrom.

The art of straightening sheet metal panels is one that is highlydeveloped and, consequently, there have been developed numerous toolswhereby the work may be accomplished with a minimum of effort. One ofthe tools necesary in this work is a stretcher which may be applied toopposite edges of a sheet metal panel in order that the latter may bestretched to facilitate the removal of dents or other deformationstherefrom. These stretching devices all take the form of a pair ofclamps which may be afiixed in one manner or another to opposite edgesof a sheet steel panel to be stretched, and means to push the clampsapart so as to stretch the metal extending therebetween. Thesestretching tools of prior art have in the main employed clamps whichmust be tightened down upon so as to grip the metal to be stretched and,consequently, if they are not tightened down sufiiciently, they tend toslip and gouge the metal when it is necessary to employ extremely heavyjacking forces to move them apart.

It is appreciated that stretching tools having automatically operatedclamps have been ,devised wherein the means required to move them aparthas also been utilized for tightening the grip of the clamps upon themetal to be stretched. However, these last-mentioned devices or toolshave been of unduly complicated construction which are costly tomanufacture and are relatively difficult to operate.

The present invention relates to the last-mentioned type of stretchingtool which is of relatively simple construction, being easy to affix tothe metal to be stretched and to operate, which is readily adjustable topanels of varied sizes and thicknesses, yet which is relativelyinexpensive to manufacture and maintain.

The present invention comprises an elongated guide member, a pair ofclamps mounted on the guide member for engagement with opposite edges ofa panel to be stretched, at least one of said clamps being movablelongitudinally thereof, said clamps each having a stationary jaw elementand a movable jaw element pivotally mounted thereto for movement betweenopen and gripping positions, and an extensible jack extending betweenthe movable jaw elements for simultaneously moving the latter into theirgripping position and pushing the clamps apart.

Referring to the drawings which illustrate the invention,

FIGURE 1 is a side view of the invention,

3,427,850 Patented Feb. 18, 1969 FIGURE 2 is an enlarged end view of theinvention taken in the direction 2-2 of FIGURE 1, and

FIGURE 3 is a top plan view of the invention.

Referring to the drawings, the stretching tool therein illustratedcomprises in general a pair of clamps 10 and 11 slidably mounted on anelongated cylindrical guide rod 12 for movement in a direction away fromand towards each other and arranged to grip opposite edges 15 and 16respectively of a sheet metal panel 18, such as an automobile door orthe like, said clamps being arranged to be pushed apart by means of anextensible jack 20 so as to stretch the metallic panel and therebyfacilitate the removal of dents or other deformations therein.

The clamps 10 and 11 are of substantially but counterposed identicalconstruction, accordingly, the same numerals will be used to identifyidentical components in each. Each clamp comprises a pair of jawelements 23 and 24 which are pivotally interconnected and which may bepivotally moved between open and gripping positions. Jaw element 23which, for the purposes of the specification and claims following, shallbe termed the stationary jaw, is of L-shaped construction and forms apair of arms 26 and 27, arm 26 being elongated and having secured at itsfree end 28 an elongated cylindrical sleeve 30, whereas the free end ofarm 27 is provided with a gripping element 32 having a serrated face 33.Jaw element 24 is also of L-shape configuration having arms 35 and 36,arm 35 having at its free end 38, a gripping element 39, also having aserrated face 40 which extends when the jaws are moved to their grippingposition as illustrated in FIGURE 1 in planar parallelism with the face33 of the element 32. The arm 36 is elongated and is provided with aforwardly extending hooked element 43 at its free end 44. Both the jawelements 23 and 24 are pivotally mounted on the shank 46 of a rivet 47located substantially at the juncture of the arms with each of saidjaws, the latter being spaced apart by means of a thick washer over theshank 46.

The clamps are normally urged to their gripping position by theprovision of elongated helical tension springs 50 connected between thehooked elements 43 of the arms 36 and engaged through suitable aperturesin arms 26.

The guide rod 12 is preferably formed of a length of cylindrical tubularpipe into one end 52 of which is threadedly inserted a plug 53 having aradially extending annular flange 53 of larger outside diameter than theoutside diameter of the guide 12.

The outside diameter of the guide 12 is suflicient to permit it to beslidably and rotatably inserted through the sleeves 30 of both of theclamps so that the clamps may depend freely therefrom, both clamps beingarranged so that the jaw elements 23 and 24 of one extend towards thecorresponding jaw elements of the other with the sleeve 30 of clamp 11abutting the flange 54 of plug 53.

In the use of the tool, the panel 18 is located between the clamps 10and 11 as illustrated in FIGURE 1, the tension springs serving to impartan initial grip of the jaw elements with the opposite edges of thepanels. The extensible jack 20 which, in this particular case isillustrated as a hydraulic type having a piston rod 55 and cylinder 56,is extended between the arms 36 of both clamps and hydraulic fluidemitted into the cylinder 56 via the conduits 57. This tends to causerotation of the jaw elements 24 about their pivotal axes, tighening thegrip of the clamps upon the panel 18 and at the same time exertingsuflicient pressure so as to move clamp 10 away from clamp 11, therebystretching the panel extending therebetween. With the construction ofthe tool as hereinbefore described, it will be seen that the grippingforce of the jaw elements upon the panel is a direct function of theforce required to move the clamps apart, the proportionate length ofarms 35 and 36 of the jaw element 24 being arranged so that the grippingforce imposed upon the panel is never excessive, being sufficient onlyto hold the jaws in place against the force necessary to spread theclamps apart.

Occasionally, in order to properly repair the damaged panel, it isnecessary to remove the jack in order to provide Working room over thedamaged area, In order, therefore, to maintain the panel in stretchedcondition, clamp is fitted with a locking device 60 which is arranged soas to be inoperable when the jack is operated to spread the clamps apartand which will automatically grip the guide rod 12 and prevent movementof the clamp 10 in the reverse direction.

This locking device comprises an annular plate 61 having a pair ofdiametrically opposed radially extending arms 62 and 63, the internaldiameter of the plate being slightly larger than the exterior diameterof the guide rod so as to permit lateral deflection of the platethereon. The device is positioned adjacent the outer end of sleeve 30 ofclamp 10, one arm 62 extending downwardly through a longitudinallyextending slot 64 formed in an extending piece 65 secured to the arm 26of jaw element 23 of the clamp 11 so as to be slidably movable therein.The other arm 63 extends above the sleeve 30 of the lastmentioned clampand is secured to one end 66 of a tension spring 67, the other end 68 ofthe spring 67 being secured to the last-mentioned sleeve. The spring 67normally pivots the annular plate 61 about the sleeve into a laterallydeflected position, as shown in FIGURE 1, in which position the plate isurged into binding engagement with the guide rod. It will be seen thatany movement of clamp 10 towards clamp 11 will tend to result in greaterlateral deflection of the plate 61 with respect to the guide rod,thereby increasing the binding effect. Conversely, the locking device 60will not hinder the movement of clamp 10 in a direction away from clamp11 as movement in this direction will result in movement of plate 61 toa less laterally deflected position with a consequent decrease in thelatters binding effect on the guide rod.

The binding effect of the locking device 60 may of course be overcome bysimply moving the arm. 63 by hand against the action of the spring 67 toa less laterally defiected position so as to permit free movement of theclamp 10 in any direction.

What I claim as my invention is:

1. Sheet metal panel stretching apparatus comprising an elongated rigidguide member, a pair of clamps mounted on the guide member forengagement with opposite edges of a panel to be stretched, at least oneof said clamps being movable longitudinally of the guide member, saidclamps each having a stationary jaw element and a movable jaw elementpivotally mounted thereto for movement between open and grippingpositions, and an extensible jack extending between the movable jawelements for simultaneously moving the latter into their grippingposition and continued extension of said jack pushing the clamps apartalong said guide member.

2. Sheet metal panel stretching apparatus comprising an elongated rigidguide member, a pair of clamps mounted on the guide member forengagement with opposite edges of a panel to be stretched, at least oneof said clamps being movable longitudinally of said guide member, saidclamps each having a stationary jaw element and a movable jaw elementpivotally mounted thereto for movement between open and grippingpositions, a lever extending from each of the movable jaw elements forpivotally moving the latter, and an extensible jack extending betweenthe levers for simultaneously moving the jaws to their gripping positionand continued extension of said jack pushing the clamps apart along saidguide member.

3. Sheet metal panel stretching apparatus comprising an elongatedcylindrical shaft, 21 pair of clamps mounted on the shaft for engagementwith opposite edges of a panel to be stretched, at least one of saidclamps being slida-bly and pivotally connected to the shaft forlongitudinal and radial movement relative thereto, said clamps eachhaving a stationary jaw element and a movable jaw element pivotallymounted thereto for movement between open and gripping positions, alever extending from each of the movable jaw elements for pivotallymoving the latter, and an extensible jack extending between the leversfor simultaneously moving the jaws to their gripping position andcontinued extension of said jack pushing the clamps apart along saidshaft.

4. Sheet metal panel stretching apparatus as claimed in claim 3including resilient means connected to each of the movable jaw elementsnormally urging the latter into their gripping position so as to provideinitial gripping engagement of the clamps with the panel to bestretched.

5. Sheet metal panel stretching apparaus as claimed in claim 3 in whichthe jaw elements are each provided with serrated gripping surfaces.

References Cited UNITED STATES PATENTS 2,606,467 8/1952 Desjarlais etal. 72302 2,845,983 8/1958 Hanson 72302 X 2,855,972 10/ 1958 Greider72-302 2,858,872 11/1958 Hougen 72392 X 2,956,458 10/1960 Hougen 723023,015,353 1/1962 Brown 72302 3,051,217 8/1962 Hill et al. 723023,111,159 11/1963 Jenkins 72302 1,353,632 9/1920 Coons 269-254 X 756,7234/1904 Skoog 269-254 X CHARLES W. LANHAM, Primary Examiner.

E. SUTTON, Assistant Examiner.

US. Cl. X.R.

